In a cellular communication system, which handles simultaneous communication involving many users, as well as transmitting user data it is necessary to transmit control information associated with the user data. To ensure the control information will reach the handsets of all communicating users, a large number of communication resources must be used for its transmission (see, for example, Document 1: 3GPP, “Evolved Universal Terrestrial Radio Access [E-UTRA]; Physical Channels and Modulation [Release 8],” TS36.211, ver. 8.3.0 [2008]). However, since the control information streams are exclusively for control and do not include embedded user data, allocation of such a large number of resources to the control information is at the expense of user data and so can reduce throughput. To avoid such a reduction, Document 1 discloses a method for transmitting control information of variable size.
To deal with such variable-size control information, there is a means of detecting control information addressed to the handset of a particular user in control information transmitted to the handsets of all users when the size of control information for the handset of the particular user is unknown (see, for example, Document 2: 3GPP, “Evolved Universal Terrestrial Radio Access [E-UTRA]; Physical layer procedures [Release 8],” TS36.213, ver. 8.3.0 [2008]). The means disclosed in Document 2 involves a blind detection method which makes multiple attempts to demodulate control information while assuming various possible sizes of item, and determining that the control information is addressed to the handset of the user if it can be correctly demodulated. However, since considerable time and processing are required to demodulate all control information, a subset of control information to undergo attempted demodulation is determined for each user.
As well as the above techniques, there is a technique of increasing throughput by using a plurality of communication bands simultaneously (see, for example, Document 3: NTT DoCoMo, “Update Views on Support of Wider Bandwidth in LTE-Advanced,” 3GPP Technical Document, R1-083015 [2008]).
If plural communication bands are used simultaneously as disclosed in Document 3, and if the control information, as described in Document 1, in each band is detected by the blind detection method described in Document 2, the amount of control information undergoing attempted demodulation by the blind detection method increases with the number of bands. However, it is desirable to avoid such an increase in the number of demodulation attempts because of the added load it imposes.